1. Field of the Invention
The present invention relates to an exhaust system for a jet propulsion boat that exhausts engine exhaust gas into water.
2. Background Art
A jet propulsion boat is known in which a rider rides a saddle-type seat, and controls the vehicle by a steering handlebar having an accelerator lever on a right end portion of the steering handlebar, and a decelerator lever on a left end portion of the steering handlebar. An exhaust system for a conventional jet propulsion boat, an "Engine Exhaust system of Small-Sized Ship," is described in Japanese Unexamined Patent Publication No. 8-119196. This type of exhaust system will be described with reference to FIGS. 8 and 9 of this application.
FIG. 8 is a plan view of a conventional exhaust system for a jet propulsion boat. An engine 101 is mounted below a steering handlebar 100, an impeller (not illustrated) of a jet propulsion device is attached to a drive shaft 102 extending rearwardly from engine 101, and an exhaust system 105 is provided at the engine 101.
An exhaust pipe 106 extends rearwardly from a left side portion of the engine 101, and a muffler is connected to an outlet of the exhaust pipe 106 arranged on the left side of the jet propulsion device 103. A connecting pipe 108 having an inverse U shape is connected to an outlet of the muffler 107 and extends to the right side by passing over the jet propulsion device 103. An auxiliary muffler 109 is connected to an outlet of the connecting pipe 108 and is arranged on the left side of the jet propulsion device 103. An exhaust pipe 110 is connected to an outlet of the auxiliary muffler 109.
The jet propulsion boat is propelled by jetting water sucked from a hull bottom rearwardly from a nozzle 112 by rotating the impeller of the jet propulsion device 103 by the engine 101. Exhaust gas from the engine 101 is exhausted from the exhaust pipe 110 into a casing of the jet propulsion device 103 by flowing through the exhaust pipe 106 to the muffler 107. The gas then flows from the muffler 107 through the connecting pipe 108 to the auxiliary muffler 109, then out the exhaust pipe 110.
FIG. 9 is a sectional view taken along a 9--9 line of FIG. 8. FIG. 9 shows the muffler 107 and the auxiliary muffler 109 respectively arranged at portions 113 and 114 of the hull bottom on the left side and the right side of the jet propulsion device. The muffler 107 and the auxiliary muffler 109 are connected by the connecting pipe 108 having an inverse U shape.
The height H of a top portion 108a of the connecting pipe 108 can be made sufficiently high to prevent water from accidentally entering the muffler 109 from crossing over the connecting pipe 108 and entering the engine 101. Accordingly, the connecting pipe 108 is generally referred to as a water lock pipe.
However, since the auxiliary muffler 109 is attached between the connecting pipe 108 and the exhaust pipe 110, when water enters the exhaust pipe 110 and an exhaust port of the exhaust pipe 110, there is the concern that water which has entered the exhaust pipe 110 may also enter the auxiliary muffler 109.
When water enters the auxiliary muffler 109 and the volume of the auxiliary muffler 109 is reduced, the noise reduction capacity of the auxiliary muffler is deteriorated, and exhaust noise increases.
It therefore is an object of the present invention to provide an exhaust system capable of sufficiently reducing exhaust noise.